This invention relates to a conveying apparatus and to a separation apparatus.
There are a number of known apparatus for conveying material such as tobacco or tea. One apparatus is a vibratory conveyor in which the material is thrown forward by asymmetric vibration. Another apparatus is a pneumatic conveyor in which the material is carried in a high velocity air stream; in order to convey the material properly the air stream speed must be several thousand feet per minute.
Both these methods cause considerable degradation to the leaf material. This results in the creation of "dust" and reduces the percentage of the material which is useful for further processing. The dust may be created by the breakage of the leaf material into smaller pieces, and also by the separation of small particles which are attached to the leaf material. Usually expensive separation apparatus needs to be provided to collect the dust.
Reference is made to the following patent specifications, each of which discloses the conveying of a material using an air stream: EP-A-189005; U.S. Pat. No. 4,033,555; FR-A-2553072; DE-C-88402; and U.S. Pat. No. 2,882,097.
Conventionally, air-borne matter such as matter conveyed by a low pressure pneumatic conveyor is separated from the air stream by a mechanical device, such as a cyclone. These devices, however, are generally large and expensive items of equipment.
In GB-A-1,095,904 there is described an air filtering apparatus which is particularly suitable for removing fibre waste from an air stream. The apparatus has an inlet, an air outlet and a waste outlet. An air permeable screen is disposed between the inlet and the air outlet; the air permeable screen is not permeable to the fibre waste.
In GB-A-1,122,705 there is described an apparatus for separating solid particles entrained in a gas stream. As with GB-A-1,095,904 the apparatus includes an inlet, a gas outlet, a solid particle outlet, and a gas permeable screen disposed between the inlet and the gas outlet. The screen can be formed of a perforated sheet metal or a wire mesh.
Another apparatus for separating air-borne matter from an air stream is described in GB-A-1,575,175.
When designing this type of separation apparatus it is advantageous for the separator to be as small as possible in order to reduce manufacturing costs, and to reduce the amount of space taken up by the separator.
However, when the apparatus is made smaller the air-borne matter tends to accumulate on the screen and this increases the load on the fan forcing the air through the separator. This problem is solved in GB-A-1,575,175, where the structure of the separator is carefully selected to reduce to a minimum any accumulation on the screen.
Another type of separation apparatus, known as an elutriator is disclosed in EP-A-159890.